1. Field
This invention relates to silver recovery systems for the recovery of the silver values from solutions used in the development of silver containing films such as X-rays, photographic, graphic arts and the like by automatic processing machines.
2. Prior Art
Processing of silver-containing films results in substantial amounts of silver being removed from the films. In some black and white films as much as 60% to 80% of the silver is dissolved from the film while in most color films substantially all the silver is removed. Recovery of this silver has become imperative for economical film processing. The silver values derived from x-ray films and the like during automatic processing have been heretofore collected as shown in FIG. 1 which illustrates a somewhat typical prior art apparatus wherein an overflow is provided from the fixer solution tank to a replaceable or removable silver recovery unit. Such silver recovery units are electrolytic units, metallic replacement units or ion exchange units wherein silver is exchanged for other ions. In the metallic replacement units, silver replaces iron or zinc, for example, in the solid state.
The fixer solution, usually sodium or ammonium thiosulfate, removes all of the unreactes ilver from the film. The fixer tank is located immediately after the developer tank. The developer causes the exposed silver to react. The fixer solution is periodically pumped from a fixer solution storage tank by a small metering pump to renew solution in the fixer tank for each film fed into the processor. This is done in an effort to maintain a substantially balanced concentration of fixer solution in the processor. Some of the developer solution from the developer tank is carried over into the fixer tank with the film and would soon completely dilute and neutralize the effectiveness of the fixer solution. An overflow is provided from the fixer tank to a silver recovery unit. Thus, as developer solution is carried into the fixer tank and as renewal solution is metered from the fixer storage tank, the fixer solution in the fixer tank overflows.
Whenever the fixer tank is emptied for periodic maintenance, such as cleaning of rollers and the like or for repair of any malfunctioning part or because of any imbalance of chemical in the fixer tank, those silver values in the solution are lost to the main drain. Also, in refilling an empty fixer tank the metering pump is not used since it is sized to maintain liquid levels and not to refill the tanks. Buckets are used to refill the fixer and developer tanks. Since the fixer tank is in very close proximity to the developer tank and the wash tank, both of which have open tops, refilling of the fixer tank must be very carefully done to prevent contamination of the developer solution or the wash water. As little as four ounces of fixer in a two to five gallon tank of developer inactivates the developer solution.
Another technique for silver recovery (not illustrated) involves an electrolytic unit wherein the overflow of solution from the fixer tank is continuously directed to an electrolytic silver recovery unit which removes silver from the solution and then returns the solution to the fixer tank. Whenever such a fixer tank is emptied for periodic maintenance or repair, the silver values in the tank are again lost to the sewer.